The present invention relates to a method for controlling the pressures at which fluid-operated extensible and collapsible props arranged between the sole plate of a mine roof support engaging the sole of a mine gallery and a roof shield engaging the roof of the mine gallery press the roof shield against the roof of the mine gallery, and in which the fluid pressure in the props is controlled corresponding to the distance between sole plate and roof shield while overloading of the mine roof support is avoided.
The present invention relates also to an apparatus for carrying out the method.
In mine roof supports, which are especially used in mine galleries in which coal seams are mined, the roof shield and the sole plate are held spaced from each other by pivotally connected fluid-operated extensible and collapsible props to transmit the force of the fluid-operated props to the sole of the mine gallery and to the roof thereof. Since the thickness of the coal seams to be mined often varies considerably at successive stretches, so that the distance between the sole plate and roof shield has to be adjustable within a wide range, the props are usually arranged inclined to the sole plate at an angle differing from 90.degree.. The props transmit therefore in their inclined position only a component of their force to the roof of the mine gallery, which is normal to the roof, so that they must be constructed correspondingly large to produce the necessary forces. The inclination of the props relative to the sole plate changes with the distance of the roof shield from the sole plate. At a greater distance between the sole plate and roof shield, the props are inclined less to the sole plate than at a smaller distance. Correspondingly, the component of the supporting force of said props which is normal to the roof shield is larger at a greater distance between roof shield and sole plate than at a smaller distance between these two components, so that the various elements of the mine roof support, such as the roof shield, the sole plate and the rear shield, have to be correspondingly strongly constructed in order to absorb also the higher mechanical stresses occurring at a large distance of roof shield and sole plate from each other. Such an overdimensioning of the various components of the mine roof support requires not only higher manufacturing costs, but is also detrimental during transport of the mine roof support, during use and maintenance of the same.